The Department of Health has asked the Advisory Committee of Dangerous Pathogens to see if the current guidelines about contact with animals are satisfactory.

The committee is due to meet in October and is expected to discuss how the outbreak has been handled.

A DOH spokesman said: “It will review whether there is a need to change the current guidance or a need for additional precautions.

“The risk of infection from E-coli 0157 through petting farm animals can be prevented by following everyday good hand hygiene measures.

"Ill health following a visit to an open farm is unusual even among children and these risks need to be balanced against the benefits for a child's education and development that arise from contact with animals."

The HPA has already announced an investigation into the outbreaks of infection.

An HPA spokeswoman said the number of cases at Godstone - which closed its gates on September 12 and traced its first link of infection back to August 8 – rose from 57 to 64 over the weekend.

The children remaining in hospital are all described as stable. Among them are two-year-old twins Todd and Aaron Furnell, from Tonbridge, Kent, who were both being treated on dialysis machines.

Two medical experts have voiced concern about the existing guidelines regarding contact with animals, calling either for them to be reviewed or for greater controls to be introduced.

Prof Pennington said youngsters were "the most difficult part of the population to get to wash their hands" while also "most likely to touch the animals".

“We have to look very, very seriously at the guidelines that we have been running for many years and see if they need changing,” he said.

"There is an issue here and I think the public expects that we have a really good look at the guidelines and also at the way the guidelines are being implemented - it is all very well having guidelines if people are not following them.”

Professor Ron Cutler, deputy director of Biomedical Science at Queen Mary, University of London, said: "The trouble with today is often they (children) don't get to touch live animals and when they do, maybe the actual conditions in which they touch them aren't as good as they ought to be."

He said zoos should think about giving people nail brushes to make sure their hands were clean after a visit.

"One of the research projects we're doing is looking at getting the whole hand-washing system quicker and more efficient, which even for an adult is incredibly difficult.

"One thing I think we should be looking at is routine screening the animals that they actually deal with, not just stopping them from dealing with it completely."

Godstone Farm’s sister farm, Horton Park Children's Farm in Epsom, White Post Farm in Nottinghamshire and The World of Country Life farm, in Exmouth, Devon, have all been closed.

Symptoms of E-coli include diarrhoea and vomiting and can lead to kidney failure.